In April 2012, the White House highlighted Nancy Clark, who runs a small marketing firm in North Conway, N.H., and was a believer in tax credits being offered to small businesses to help cover employees under the health care law. Last fall, Republicans pointed to Ms. Clark’s concern that her employees’ insurance premiums had shot up by 39 percent and that she was having fits trying to gain access to Healthcare.gov.

In the end, Ms. Clark said last week, all her employees were able to obtain health care through the federal marketplace, with better benefits at or below the cost of her old policies. But she was subjected to some remarkable abuse.

“Over the course of my career, I’ve been quoted here and there, but never have I gotten what I got,” she said. “Just a lot of extreme stuff, and it was disappointing and disconcerting” — including vicious postings on the company’s Facebook page and calls to the office.